Monolayer GeSe Research Articles

Effect of p-block metal doping on the optical properties of blue-phosphorene phase monolayer GeSe

Expanding the optical absorption of blue-phosphorene phase GeSe and designing it as infrared light driven photocatalysts and photodetectors is of particular significance. In this work, the mechanism of p-block metals (Al, Ga, In, An, Pb, Sb and Bi) doping enhancing the optical performance of monolayer blue-phosphorene phase GeSe was investigated. The effect of all p-block metal doping on the lattice constant of GeSe is very weak. Pb doped system has the smallest formation energy (−4.82 eV). Except for Sn and Pb, other p-block metal doping can introduce deep impurity levels into the band gap of monolayer GeSe, and they can significantly absorb infrared light, especially Ga doped systems. This is due to the emergence of impurity levels that assist the photon transition. The results of this work provide guidance for promoting the application of blue-phosphorene phase GeSe in the field of photocatalysts and photodetectors.

Two-dimensional GeSe monolayer doped with single main-group element atom for hazardous gas detection: A first-principles study

Currently, the identification of sensing materials that can selectively and rapidly respond to hazardous gases is urgent for safeguarding the environment and human life. The adsorption of hazardous gas molecules (NO, NO2, SO2, CO, and H2S) on the GeSe monolayer doped with single main-group element atom is investigated and compared based on first-principles density functional theory (DFT). NO2 has the highest adsorption energy and charge transfer adsorbed on both pristine GeSe and doped GeSe monolayer. At ambient temperature, for any doped GeSe monolayers adsorbing gas molecules (including H2O, O2, and N2), the occupation function value of NO2 is the highest. The analysis of density of states (DOS) and band structure indicates that NO2 interacts with different modified GeSe monolayers in terms of atomic orbitals. Moreover, Al-GeSe has the largest change of work function before and after the adsorption of NO2, meaning that Al-GeSe has the greatest response to NO2. current-voltage (I-V) characteristics demonstrate that Al-GeSe exhibits a remarkable current change after the adsorption of NO2. These results illustrate that Al-GeSe has a strong physical and chemical interaction with NO2, yielding a high response and selectivity, which is anticipated to be the optimal gas sensing material for NO2.

Photocatalytic water splitting of polarized GeS/Zr2CO2 heterostructure by biaxial strain engineering

Type-II heterostructures have gained popularity in photocatalysis due to their ability to suppress carrier recombination. One distinctive approach towards achieving superior photocatalytic efficiency is by constructing heterostructures using 2D polarized materials. In this work, we constructed a GeS/Zr2CO2 heterostructure and investigated its built-in electric field and photocatalytic properties using first-principles calculations, with a focus on the effects of biaxial strain engineering. Our results indicated that under biaxial tension, the band alignment of GeS/Zr2CO2 heterostructure changed from a type-I to a type-II, while maintaining an indirect band gap. The GeS/Zr2CO2 heterostructure possessed a built-in electric field induced by dipoles and interfacial effects from the GeS monolayer and the interface between two monolayers, respectively, which increased with biaxial tension. Additionally, the GeS/Zr2CO2 heterostructure exhibited superior light absorption compared to individual monolayers, which was further enhanced by biaxial tension. The stretched 3% (4%) GeS/Zr2CO2 heterostructure has a remarkable STH efficiency of 21.2% (20.6%). Moreover, their anisotropic me* and lower mh* can enhance the efficiency of photocatalytic reactions by suppressing carrier recombination. These results suggest that the GeS/Zr2CO2 heterostructure hold great potential as water-splitting photocatalysts, and biaxial strain is a promising approach for developing high-performance photocatalysts in the foreseeable future.

Mn-X (X = F, Cl, Br, I) Co-Doped GeSe Monolayers: Stabilities and Electronic, Spintronic and Optical Properties.

GeSe monolayer (ML) has recently attracted much interest due to its unique structure and excellent physical properties that can be effectively tuned through single doping of various elements. However, the co-doping effects on GeSe ML are rarely studied. In this study, the structures and physical properties of Mn-X (X = F, Cl, Br, I) co-doped GeSe MLs are investigated by using first-principle calculations. The formation energy and phonon disspersion analyses reveal the stability of Mn-Cl and Mn-Br co-doped GeSe MLs and instability of Mn-F and Mn-I co-doped GeSe MLs. The stable Mn-X (X = Cl, Br) co-doped GeSe MLs exhibit complex bonding structures with respect to Mn-doped GeSe ML. More importantly, Mn-Cl and Mn-Br co-doping can not only tune magnetic properties, but also change the electronic properties of GeSe MLs, which makes Mn-X co-doped GeSe MLs indirect band semiconductors with anisotropic large carrier mobility and asymmetric spin-dependent band structures. Furthermore, Mn-X (X = Cl, Br) co-doped GeSe MLs show weakened in-plane optical absorption and reflection in the visible band. Our results may be useful for electronic, spintronic and optical applications based on Mn-X co-doped GeSe MLs.

2D/2D Janus BiTeCl/GeSe vdW heterostructure as a robust high-performance S-scheme photocatalyst for water splitting

Two-dimensional (2D) S-scheme van der Waals (vdW) heterostructures (HSs) have aroused much interest as advanced photocatalysts due to their strong redox ability and light utilization. In this work, we have proposed a 2D/2D vdW HS composed of Janus BiTeCl monolayer (ML) and GeSe ML, and systematically investigated its photocatalytic performance using first-principles calculations. Our results show that the HS exhibits an appropriate electronic band in which the existence of intrinsic built-in electric field from GeSe ML to BiTeCl ML enhances the separation of photo-induced electron-hole pairs and certifies a S-scheme mechanism in the HS. Furthermore, the optical and electronic properties of the HS are nearly independent of either biaxial or uniaxial strain, showing robustness of the HS applied in an ever-changing environment. Notably, the HS can achieve spontaneously solar-driven water splitting and exhibits an enhanced solar-to-hydrogen (STH) efficiency up to 19.27 % owing to its S-scheme mechanism and wide range of light absorption with high absorption coefficient. Our results give insights to the structure, electronic and photocatalytic properties of 2D/2D Janus BiTeCl/GeSe vdW HS and may provide a promising S-scheme photocatalyst for overall water splitting.

Ultrahigh Carrier Mobility in Two-Dimensional IV-VI Semiconductors for Photocatalytic Water Splitting.

Two-dimensional materials have been developed as novel photovoltaic and photocatalytic devices because of their excellent properties. In this work, four δ-IV-VI monolayers, GeS, GeSe, SiS and SiSe, are investigated as semiconductors with desirable bandgaps using the first-principles method. These δ-IV-VI monolayers exhibit exceptional toughness; in particular, the yield strength of the GeSe monolayer has no obvious deterioration at 30% strain. Interestingly, the GeSe monolayer also possesses ultrahigh electron mobility along the x direction of approximately 32,507 cm2·V-1·s-1, which is much higher than that of the other δ-IV-VI monolayers. Moreover, the calculated capacity for hydrogen evolution reaction of these δ-IV-VI monolayers further implies their potential for applications in photovoltaic and nano-devices.

Theoretical study on the negative differential resistance behavior of N-doped GeSe monolayer

Using a combination of non-equilibrium Green’s function (NEGF) and density functional theory (DFT), the electronic structures and transport characteristics of N-doped GeSe monolayer were investigated systematically. The calculated band structures illustrated that the doping of N atoms changed GeSe monolayer from a semiconductor to a metal. Further, a clear negative differential resistance behavior (NDR) was found in the voltage-current curves of the N-doped GeSe based devices. Moreover, the current peak-to-valley ratio (PVR) varied with the doping concentration of N atoms. As the doping concentration decreased, the peak of NDR shifted toward the millivolt region. Especially, the NDR behavior with a PVR up to 103 entered the mV bias region when the doping concentration was reduced to 0.69%. These results provide a novel approach to design the low power nanodevice based on the GeSe monolayer.

Near-Field Radiative Heat Transfer between $\\beta-$GeSe monolayers: An ab initio study

ABSTRACT We present a theoretical study of the near-field radiative heat transfer (NFRHT) between two -GeSe monolayers, each at a different temperature. (This is a relevant 2D material with superior electron transport and optical properties compared to black-phosphorus monolayers). The required optical conductivity of the monolayer is calculated using density functional theory including spin-orbit coupling, and using the Perdew-Burke-Erzenhof parametrization. Both the intra and interband transitions are taken into account, as well as the contribution of the optical phonons. This allows us to obtain more realistic predictions of the NFRHT between two monolayers of GeSe. The role of the electron doping concentration and the plasma relaxation frequency is investigated, showing a non-monotonic dependence on the radiative heat transfer with increasing doping, and having an optimal doping where the heat flux is maximize. A strong optical anisotropy in the electric conductivity is obtained from the contribution of both electrons and ions This anisotropy is explored, showing that the relative rotation of two monolayers results in modulation of the NFRHT much larger than previously found for similar 2D materials, like -GeSe. As the angle of rotation between the monolayers increases the total heat transfer decreases. Our analysis demonstrates the relevance of properly taking into account the materialelectronic and ionic contributions.

Structures, Electric Properties and STM Images of GeSe Monolayers Doped by Group IV–VI Atoms: A First-Principles Study

Doping is an important method to modulate the physical and chemical properties of two-dimensional materials. By substitutional doping, different group IV–VI atoms are doped in GeSe monolayers to compose the doped models, of which the effects are investigated using first-principles calculations. The results show that local deformations of geometrical structure can be observed around the doping atoms. According to the analysis of the formation energy and the cohesive energy, all the doped models have a strongly bonded network, and GeSe_N possesses the most stable structure. Only the bandgap of Ge_As is direct, while those of other doped models are indirect. Thus, direct and indirect bandgaps are alternative by doping different atoms. The structural and electronic properties, especially for the bond lengths variation around doping atoms, are explained by the charge density difference. Finally, the scanning tunnel microscope images of the doped models are analyzed for further experimental investigations. Our work provides a stimulating account by atom doping which could trigger the developments and applications of new two-dimensional materials for manufacturing microelectronic and optoelectronic devices.

Adsorption and gas-sensing properties of SF6 decomposition components (SO2, SOF2 and SO2F2) on Co or Cr modified GeSe monolayer: a DFT study

This paper first proposed to modify the GeSe monolayer by doping Co and Cr atoms and investigated the potential application in the monitoring SF6 insulation equipment. The adsorption mechanism of these three gases on Co/Cr-Gese monolayers is systematically studied based on density functional theory. The adsorption mechanism of three gas molecules on the new sensors (Co-GeSe and Cr-GeSe) was evaluated from the aspects of adsorption energy, charge transfer amount, energy band structure, molecular frontier orbital, and recovery time. The results show that Co and Cr modification can significantly improve surface activity of the intrinsic GeSe monolayer, which can make the intrinsic GeSe monolayer possess better absorption and sensing performance. Especially, the Cr-GeSe monolayer gets more sensitive to the target gas, indicating this monolayer has the prospect of becoming the adsorption material of the target gas (SO2, SOF2, and SO2F2). The reasonable adsorption energy and large change of bandgap indicate that Co-GeSe monolayer can be a potential candidate for SO2 and SOF2 sensors. In addition, this work provides theoretical guidance for the further study of transition metal-doped GeSe monolayer for detecting the decomposition products of SF6 in the field of electrical engineering.

Fe-doped SnSe monolayer: A promising 2D material for reusable SO2 gas sensor with high sensitivity

Recently, 2D materials have attracted great interest in the gas-sensing field, in which TMMC GeS, GeSe, SnS, and SnSe monolayers have been reported as promising SO2 sensing materials [Chem. Phys. Lett. 686 (2017) 83–87; Appl. Surf. Sci. 484 (2019) 33–38]. However, the transport properties, sensitivity, and recovery times of such structures related to the adsorption of SO2 molecule have not been published to date. In this work, we found that the recovery times of the pristine GeS, GeSe, SnS, and SnSe monolayers after SO2 adsorption are too short, indicating their low application possibility for SO2 sensing materials. Interestingly, the transition metals doping (Cr, Mn, or Fe) improves the recovery time of the SnSe monolayer in respect of SO2 molecules. Especially the calculated recovery time of the Fe-doped SnSe monolayer in respect of SO2 molecules at 373 K is 27 s, which is suitable for reusable gas sensors. Moreover, we first designed an SO2 gas sensor based on the Fe-doped SnSe monolayer with two Au electrodes. The NEGF formalism-based calculations show its high sensitivity to an SO2 molecule. Our results suggest that the Fe-doped SnSe monolayer is a promising 2D material for reusable SO2 gas sensors with high sensitivity.

A Theoretical Study on Adjustment of Negative Differential Resistance Effect in Monolayer GeS via Substitutional Doping

Density functional theory and nonequilibrium Green's function theory are used to systematically explore the electronic structures and transport characteristics of doped monolayer GeS with group V (N, P, As) atoms. The calculated band structures demonstrate that the doping of N, P, and As atoms results in the transformation of monolayer GeS from semiconducting to metallic properties. Further, an obvious negative differential resistance (NDR) behavior is obtained by altering the dopant atom and the doping concentration. In particular, for N‐doped monolayer GeS, the NDR behavior appears in the millivolt region as the doping concentration decreases, and the current peak‐to‐valley ratio (PVR) is up to 107 (order of magnitude 7). These findings have significant implications for future design of low‐power novel nanoelectronic devices based on monolayer GeS.

On the bending of rectangular atomic monolayers along different directions: an ab initio study

We study the bending of rectangular atomic monolayers along different directions from first principles. Specifically, choosing the phosphorene, GeS, TiS3, and As2S3 monolayers as representative examples, we perform Kohn–Sham density functional theory calculations to determine the variation in transverse flexoelectric coefficient and bending modulus with the direction of bending. We find that while the flexoelectric coefficient is nearly isotropic, there is significant and complex anisotropy in bending modulus that also differs between the monolayers, with extremal values not necessarily occurring along the principal directions. In particular, the commonly adopted orthotropic continuum plate model with uniform thickness fails to describe the observed variations in bending modulus for GeS, TiS3, and As2S3. We determine the direction-dependent effective thickness for use in such continuum models. We also show that the anisotropy in bending modulus is not associated with the rehybridization of atomic orbitals.

Tunable thermal transport properties of bilayer GeS with stacking patterns

The stacking of 2D layered materials can be an effective tool to modulate low-dimensional electronic structures and transport properties. In this work, using first-principles calculations, the thermal transport properties of a GeS bilayer are systematically investigated by solving the phonon Boltzmann transport equation. Various stacking configurations for bilayer GeS are introduced, and two dynamically stable structures are confirmed. The results indicate that the thermal transport property of the GeS bilayer can be dramatically suppressed due to a decreased phonon relaxation time, which is dependent on the stacking patterns and interlayer distances. The underlying phonon transport mechanisms and the stacking effects on the lattice thermal conductivity for bilayer GeS are further revealed through a comparative study among monolayer, bilayer, and bulk GeS. In addition, the in-plane anisotropy of the thermal transport properties is also enhanced for the GeS bilayer, which is also found to be dependent on the stacking pattern. The significantly suppressed thermal conductivity for the GeS bilayer evaluated in this work implies great potential for 2D multilayer-based thermoelectric devices and applications.

Zigzag direction nanoarchitectonics of monolayer GeSe for SO2 gas sensors with high sensitivity and selectivity: a first-principles study

Zigzag direction nanoarchitectonics of monolayer GeSe for SO2 gas sensors with high sensitivity and selectivity: a first-principles study

Size-dependent ferroic phase transformations in GeSe nanoribbons

Ferroic phase transformation in monolayer nanosheets or nanoribbons endows 2D nanoelectronic devices with novel functionalities. However, less is known how the phase transformation behaves with the system size. Combined with molecular dynamic simulations and a machine learning model, we systematically investigate the temperature induced ferroic phase transformation in monolayer GeSe nanoribbons, which exhibits remarkable size effect. Specifically, the transformation hysteresis is found continuously decreased with ribbon width at the investigated scales. In contrast, the transformation temperature of monolayer GeSe nanoribbons shows non-monotonic size-dependency, i.e., it is first increased and then decreased as we narrow the GeSe nanoribbons. We attribute this to a competition between the enhanced ripple deformation, which will promote phase transformation upon cooling, and the stronger edge effect that can suppress phase transformation. In addition, the two factors are well captured by the Landau model, which will deepen our understanding of phase transformation behaviors in 2D ferroic materials.

Enhanced shift current bulk photovoltaic effect in ferroelectric Rashba semiconductor α-GeTe: ab initio study from three- to two-dimensional van der Waals layered structures

The ferroelectric Rashba semiconductors (FERSCs) are endowed with a unique combination of ferroelectricity and the spin degree of freedom, resulting in a long carrier lifetime and impressive bulk photovoltaic (BPV) efficiency that reached 25% in organometal halide perovskites. The BPV efficiency can be further improved by using low-dimensional ferroelectrics however, it is inhibited by the ferroelectric instability in low-dimensional perovskites and toxicity along with phase instability of the lead-halide perovskites. To address these challenges, the α-GeTe could be of great importance which is the simplest known lead-free FERSC with an intrinsic layered structure. Therefore, in this work, we investigate the BPV properties of three- to two-dimensional van der Waals structures of α-GeTe by calculating the shift current (SHC). We predict that the mono (1.56 Å) and bi-layers (5.44–6.14 Å) α-GeTe with the buckled honeycomb structure are dynamically stable and possess the characteristic features of the bulk up to the nanoscale limit. The SHC of ∼70 μA V−2 is calculated in bulk α-GeTe which is 20 times larger than that obtained in organometal halides in the visible light. The SHC increases with decreasing the number of layers, reaching a maximum amplitude of ∼300 μA V−2 at 2.67 eV in the monolayer which is more than double that obtained in monolayer GeS. We find that the SHC in monolayer α-GeTe can be further enhanced and redshifted by applying a compressive strain; which is correlated with the strong absorption of the xx-polarized light, stimulated by the more delocalized p x /y orbital character of the density of states. Furthermore, in the bilayer structures, the magnitude of the SHC is sensitive to the layers’ stacking arrangement and a maximum SHC (∼250 μA V−2) can be achieved with an AB-type stacking arrangement. Combining these results with the benefits of being environmental-friendly material makes α-GeTe a good candidate for next-generation solar cells application.

First principles study of biaxially deformed hexagonal buckled XS (X=Ge and Si) monolayers with light absorption in the visible region

In the present letter, we report the structural, electronic and optical properties of hexagonal buckled GeS and SiS monolayers under in-plane biaxial strain. The hybrid functional was adopted to calculate more accurate band gaps. The calculated electronic structures using Heyd–Scuseria–Ernzerhof (Perdew-Burke-Ernzerhof) methods show that both GeS and SiS monolayers display indirect band gap of 3.30 and3.03 eV (2.49 and 2.19 eV), respectively. We show that the buckling height, electronic structure and optical absorption of hexagonal buckled GeS and SiS monolayers can be tuned by applying in-plane biaxial strain. The band gap of SiS monolayer decreases by applying the tensile or compressive strain. The band gap of GeS monolayer reaches its maximum value under -2% strain and it decreases when the structure is more compressed or stretched. Both GeS and SiS monolayers exhibit optical absorption with energy covering ultraviolet light and partial visible light. By increasing the biaxial tensile strain, the absorption in visible region is expanded and enhanced due to the red shift of absorption edge.

Thermal transport properties of monolayer GeS and SnS: A comparative study based on machine learning and SW interatomic potential models

Phonon transport properties of two-dimensional materials can play a crucial role in the thermal management of low-dimensional electronic devices and thermoelectric applications. In this study, both the empirical Stillinger–Weber (SW) and machine learning interatomic potentials are employed to investigate the lattice thermal conductivity of monolayer GeS and SnS through solving the phonon Boltzmann transport equation. The accuracy of the two types of interatomic potentials and their performance for the evaluation of thermal conductivity are verified by analyzing phonon harmonic and anharmonic properties. Our results indicate that the thermal conductivity can be predicted more accurately with a machine learning approach, while the SW potential gives rise to an overestimated value for both monolayers. In addition, the in-plane anisotropy of thermal transport properties existing in these monolayers can be confirmed by both potential models. Moreover, the origins of the deviation existing in calculated thermal conductivities, including both the effects of interatomic potential models and monolayer compositions, are elucidated through uncovering the underlying phonon transport mechanisms. This study highlights that in contrast to the machine learning approach, more careful verification is required for the simulation of thermal transport properties when empirical interatomic potential models are employed.

Gas adsorption effects of monolayer GeSe in terms of anisotropic transport properties

Two-dimensional layered semiconducting material germanium selenide (GeSe) has attracted significant attention due to its environmental friendship, anisotropic electronic structures, and strong air-stability. To evaluate the candidacy of monolayer GeSe as a potential gas sensing material, the adsorption characteristics of various small gas molecules on monolayer GeSe are comprehensively studied combining density functional theory calculations and non-equilibrium Green’s function formalism. The charge transfer reaction between gas molecules and monolayer GeSe leads to the marked change of the carrier density, which further affects the anisotropic transport characteristics of monolayer GeSe. The calculated band structures and I–V curves reveal distinctive responses of monolayer GeSe to the different gas molecules, and higher sensitivity of the monolayer GeSe in presence of SO2, NH3, NO2 gas molecules along the zigzag direction is obtained. These results suggest that monolayer GeSe along the zigzag direction has promising application in gas detector.